At the present time, vehicle door handles are equipped with devices for detecting a user's presence. The detection of a user's presence, combined with the recognition of a “hands-free” remote access control badge worn by the user, enables the openable body sections of the vehicle to be locked and unlocked remotely. Thus, when the user wearing the corresponding electronic badge identified by the vehicle approaches the handle or touches the door handle of his vehicle, the openable body sections of the vehicle are automatically unlocked. When the user approaches or presses on a precise location on the vehicle door handle, called the “unlocking area”, the door opens without any need to unlock it manually. Conversely, when the user, still wearing the necessary badge and identified by the vehicle, wishes to lock his vehicle, he closes the door of his vehicle and approaches or momentarily presses another precise location on the handle, called the “locking area”. By means of this gesture, the openable body sections of the vehicle are automatically locked.
These presence detection devices usually comprise two capacitive sensors, in the form of two electrodes connected electrically to a printed circuit and integrated into the handle, each in a precise locking or unlocking area. Usually, one electrode is dedicated to each area; that is to say, one electrode is dedicated to the detection of the approach and/or the contact of the user's hand in the locking area, and one electrode is dedicated to the approach and/or the contact of the user's hand in the unlocking area. When supplied with power, an electrode emits an electric field which defines a detection area (a locking area or an unlocking area). The approach of a user's hand to this detection area perturbs this electric field and changes the capacitance as seen by said electrode. By measuring the variation of this capacitance, it is therefore possible to detect the approach of the user's hand to said area, that is to say toward the handle in the present case. When this detection has taken place, the capacitive sensor then sends an unlocking or locking instruction to the door unlocking and locking system.
The two areas, for locking and unlocking, are located at different points on the handle, and the electric fields emitted by the respective electrodes must not overlap.
More precisely, for each detection electrode, a high level of detection sensitivity in its respective area is desirable, to avoid non-detection (where detection does not take place when the hand approaches the electrode).
For this purpose, there is a known way of positioning a conductive element (such as a copper sheet) connected to the electrical ground on the side of the electrode where detection is not desired. This conductive element connected to the ground attracts the electric field emitted by the electrode, and provides shielding from the electric field emitted by said electrode on the side where the element is located.
As there is limited space in a vehicle door handle, there is a known way of integrating the conductive element and the two electrodes into each of the two faces of the printed circuit respectively.
Purely for the purposes of explanation, only one electrode will be discussed here, this being the electrode dedicated to the unlocking area. A prior art device is described with reference to FIG. 1.
FIG. 1 shows a door handle 10 of a motor vehicle (vehicle not shown) in which a device D for detecting a user's presence is located. The detection device D is supplied with a voltage of Vcc and is grounded by an electrical connection L connected to the vehicle V.
Said door handle 10 comprises a first outer surface S1 oriented toward the door (not shown) and a second outer surface S2, opposed to the first surface S1 and therefore oriented toward the opposite side from the vehicle, or more precisely toward the user (not shown). This detection device D comprises a first unlocking electrode 12, having one face located near the first outer surface S1, a locking electrode 14 located near the second outer surface S2, control means 13, and a conductive element 11 having one face located near the second outer surface S2. The unlocking electrode 12, the locking electrode 14 and the conductive element 11 are connected to the control means 13. The control means 13 comprise electronic components, and measure the capacitance seen by the electrode 12 in order to detect a user's presence. The conductive element 11 is connected to the ground by the control means 13 and provides a shielding function. These control means 13 are, for example, a printed circuit comprising a microcontroller 20 (not shown). This detection device D defines a detection area A (which is the unlocking area in the example shown in FIG. 1) located between the first outer surface S1 and the vehicle door, and having dimensions which are estimated in a reference frame formed by three perpendicular axes X, Y, Z. In the rest of the description, only the unlocking electrode 12 dedicated to the unlocking area A will be considered, although the invention is also applicable to the electrode dedicated to the locking area (not shown). As shown in FIG. 1, the unlocking area A is considered to be an area located between the handle 10 and the vehicle. This unlocking area A is also called the “sensitivity” of the detection device D.
The conductive element 11, located between the second outer surface S2 and the unlocking electrode 12, therefore provides detection of the approach of the user's hand in the unlocking area A only; in other words, it provides detection toward the first outer surface S1, and prevents any approach detection on the front face of the handle P, that is to say toward the second surface S2.
However, the proximity of the conductive element 11 to the electrode 12 creates strong electromagnetic coupling between the electrode 12 and the electrical ground, as a result of which the detection sensitivity of said electrode 12 is reduced.
In other words, the unlocking area A, which extends from the unlocking electrode 12, is small, and does not cover the space between the first outer surface S1 of the handle P and the surface of the door S′ located opposite (see the surface S1).
Thus the user's hand will not be detected if it is located nearer to the surface of the door S′ than to the first outer surface S1.